Conventionally, organic coated substrates are cured in hot air ovens in which the substrate is exposed to temperatures in the range of 150-210 degrees Centigrade for a dwell time of about 10-20 minutes. This conventional curing technique involves the disadvantage that the carrier solvent of the coating is evaporated and produces harmfull air pollution if released to the atmosphere. Also, efficiency considerations, due to the relatively long baking time required, generally dictate the use of very large and cumbersome ovens.
In practice, most of the hot air containing the solvent vapors is normally recirculated for energy conservation considerations and as a result, the solvent vapors must be incinerated, at a significant cost in energy.
Water based coatings have been developed in an effort to reduce the air pollution resulting from curing. These coatings also include a small proportion of organic solvents and are only suitable for a limited range of applications.
In U.S. Pat. Nos. 4,680,871 and 4,694,586 of the present applicant there are described and claimed apparatus and techniques for drying or curing a coating on a metal substrate such as a drum wall cylinder. In FIG. 2 of both patents and in the accompanying discussion in the specification there is shown apparatus for curing a coating on a metal substrate including apparatus for inductively heating the coated substrate in a confined space and apparatus for condensing evaporated liquids.